ECONOMIC EXPANSION SEEN FOR '87

By SUSAN F. RASKY

Published: January 5, 1987

Almost in spite of itself, the United States economy will continue to expand in 1987, marking the fifth year of unbroken growth, according to forecasts by the Reagan Administration, the Federal Reserve Board and private economists.

But the pace of growth will hardly be robust. The consensus among the 51 forecasters monitored by the Blue Chip Economic Indicators newsletter is that the economy will grow by 2.5 percent in 1987, about the same as it did in 1985 and 1986.

In practical terms, that is a pace too sluggish to lower the 7 percent unemployment rate, and neither will it succeed in generating enough new tax revenues to help reduce the Federal budget deficit. It is also too weak a growth rate to sustain the level of increases in the standard of living that Americans had come to expect. A Sustained Performance

Only twice in the postwar era -throughout most of the 1960's and again in the late 1970's - has the economy sustained itself for more than five years without tipping, or lurching, into recession.

For certain regions of the country, of course, talk of a fifth year of expansion is hardly relevant. ''When you talk about the economic outlook for 1987, it's very much a case of 'how you stand depends a lot on where you sit,' '' said James E. Annable, chief economist for the First National Bank of Chicago.

In the oil patch of the Southwest, the hope, for now at least, is that the recent firming in oil prices will persist. That may not make the regional economy much better, but at least it will prevent it from gettng worse. Sagging Commodity Prices

In America's Farm Belt, 1987 marks the sixth year of sagging commodity prices and shrinking foreign markets. Yet, the Farm Belt states have become less and less dependent on agriculture, and, like the rest of the country, now derive the bulk of their income from service industries. That diversification means their economies are expected to hold their own this year, growing more slowly than the nation as a whole, but avoiding recession.

Perhaps the most striking feature about the growth economists expect this year is the shift in the forces that will be driving it.

''We are going to be moving from a situation where consumption spending is the overwhelming engine of growth to one where it is passive,'' Mr. Annable said. In place of consumer spending, he and other economists look for a significant improvement in the trade deficit, already a record $159 billion in 1986, with a final month of figures yet to be reported. Assumptions About Currency

Their assumption is that the dollar has weakened sufficiently against European and Japanese currencies to make American exports more competitive in markets abroad.

''I think it's a safe bet that by Labor Day we're going to be seeing news magazine cover stories about how U.S. industry is back,'' said Georges F. Rocourt, chief economist for the Mercantile Savings Deposit and Trust Company in Baltimore. Mr. Rocourt, who believes that the economy will remain very weak despite the improvement in trade, said the improvement in manufacturing would be hastened by a push in Congress to pass protectionist trade measures and industrial policy legislation.

Edward Guay, chief economist of the Cigna Corporation, said the changes in the tax law would also help manufacturing because they would direct capital away from nonproductive uses.

''Although many businesses are reluctant to lose the investment tax credit, it is a serious mistake to view the overall legislation, or even the loss of the I.T.C., as negative,'' Mr. Guay said.

The catch in all this is that consumers, who spent at economic-boom levels in 1986, may retreat because of heavy debts or a loss of confidence before the benefits of an improved trade position take hold.

Forecasters spent much of the last year waiting in vain for a lower dollar to translate into a rise in exports and a decline in imports that would lift the economy out of the doldrums. But trade figures released on Wednesday showed a staggering $19.2 billion deficit for November, which reversed a three-month improvement in trade flows. Fear of a Recession

''If the consumer falters or the trade situation fails to turn around as expected, the economy could easily side into a recession,'' said John O. Wilson, chief economist for the Bank of America. His forecast calls for fixed investment by business to be negative because of the tax changes and a leveling off in housing activity.

The budget deficit will make no contribution to growth in 1987, Mr. Wilson said, leaving consumer spending and trade as the only potential sources of growth. He is counting on the consumer to hang in through 1987, despite large debts.

While the ratio of home mortgage and consumer debt outstanding to disposable personal income reached historic highs in 1986, Mr. Wilson also notes that consumers have seen substantial increases in the value of their financial assets, such as stocks.

Nevertheless, he shares with other forecasters and economists a nagging feeling that the economy cannot limp on like this forever.